High purity nitrogen at superatmospheric pressure is used in a number of applications such as blanketing, stirring, transporting and inerting in many industries such as glassmaking, aluminum production and electronics. In addition large quantities of nitrogen are used in enhanced oil or gas recovery operations after booster compression to high pressures.
One important method for producing nitrogen at elevated pressure is by the cryogenic rectification or separation of air using a single column. A disadvantage with such a system is that it can efficiently produce elevated pressure nitrogen only at relatively low recovery rates. Generally single column systems can efficiently recover only about 42 percent of the feed air as product elevated pressure nitrogen.
The recovery of nitrogen by the cryogenic separation of air can be increased by employing a double column cryogenic rectification system wherein a higher pressure column and a lower pressure column are in heat exchange relation. While such a system improves nitrogen recovery, a significant amount of the nitrogen recovered is at a lower pressure. Thus, if elevated pressure nitrogen is required, the lower pressure nitrogen must be compressed to the higher pressure thus adding both capital costs and operating costs to the nitrogen production system.
It is thus desirable to have a system which can produce elevated pressure nitrogen with improved recovery.
Accordingly it is an object of this invention to provide a method for producing elevated pressure nitrogen by the cryogenic rectification of air with improved recovery.
It is another object of this invention to provide an apparatus for producing elevated pressure nitrogen by the cryogenic rectification of air with improved recovery.